This invention relates to apparatus and method for gripping and lifting sections of concrete pipe wherein gripper arms are first locked in position for transport and then unlocked for a next pipe lifting operation without manual manipulation of the gripping apparatus.
The prior art includes lifting tongs having pivoted depending gripper arms and upwardly diverging links extending therefrom that are connected through converging pivotal links to an upper pivotal connection. U.S. Pat. Nos. 1,825,179, 1,966,240, 3,945,676, 4,023,848, and 5,842,729 are exemplary of the prior art. The prior art includes the use of an auxiliary line for operating a latch securing the gripper arms in open position.
The prior art further includes a concrete pipe lifter by KENCO of Ligonier Valley, Pa. that utilizes opposed gripper arms joined by a pivot disposed longitudinally of the concrete pipes and having diverging upwardly extending links. The diverging links are connected by pivoted converging links to a pivot point at a lower end of an upright connector or operator plate. The connector plate has a fastener at its upper end for securement to suitable power operated lifting or hoisting apparatus that includes a linear connector such as a hook and cable. Latches are provided for securing the linkage in fixed open position for transport. However, the latches must be released manually for permitting the gripper arms to grip and carry a pipe. The latches have pivotal connection at the pivot point at the lower end of the connector plate, maintaining the gripper arms in spread relation for lifting a concrete pipe or other elongated object for transport preparatory to a next pipe lifting operation. The latches may then be manually freed to release the gripper arms for the next lifting operation.
The KENCO pipe lifter is capable of lifting concrete pipes within a limited range of sizes. However, because there is only a single latched position permitted by the manually operable latches the gripper arms must be opened by a fixed amount to accommodate the largest pipe size. The large fixed opening of the gripper arms requires that the ditch for receiving the pipe be of sufficient width to accommodate the largest pipe size even though a relative small pipe is to be placed in the ditch. Because of the large fixed opening, the gripper arms are capable of exerting only a limited gripping action on pipes of small sizes thus resulting in slippage of the concrete pipes. Moreover, manually operable fastening means are very difficult to manipulate in normal use in pipe laying.
Accordingly, it is an important object of this invention to provide pipe lifting apparatus and method suitable for use on a range of concrete pipe sizes permitting several opening spacings between the gripper arms to assure an effective gripping action on a relatively broad range of pipe sizes and avoid excessive spacing as would necessitate a ditch of inordinate size to accommodate a relative small pipe.
Another important object of the invention is the provision of apparatus including opposed pivoted gripper arms having a pivoted operator member extending upwardly for attachment to a lifting cable and the like wherein stops are provided for selective locking and unlocking responsive to manipulation of the operator member transversely of the pipes for fixing the gripper arms automatically for transport to a location for a next pipe laying sequence. The operator member is manipulated by movement as by a lift cable from side to side as needed for engagement and release of the respective stops.
Still another important object of the invention is the provision of opposed adjustable auxiliary wedge-shaped gripping members carried by opposed gripping arms above the center of gravity of the pipes to accommodate various sizes of pipes through an adjustable fixed gripping action.
The stop mechanism or device is operated by movement of the lift cable preferably through an upright operator member in the form of a plate longitudinally pivoted at its lower end. The stop mechanism includes transversely spaced members carried by upright links forming a stirrup having an upright locking arm pivotally connected on a lower end at a pivotal juncture of the gripper arms and having spaced pin engaging stops for receiving a transverse pivot pin extending outwardly from an upper pivotal connection aligned above the juncture of the gripper arms. The pin engaging stops are preferably carried by a locking plate adjustably positionable on the upright arm to permit locking engagement for only one pipe size per position.
A pin is provided for selective engagement within spaced holes in the links for limiting closure of the links by more than an amount desirable for engaging respective stops.
While the invention has been described in the context of laying concrete pipes it is believed that many uses for the invention will be found, for example, manipulating other elongated articles such as poles, logs, steel pipes and the like. The term lift cable has been used herein for descriptive purposes but it is to be understood that this term encompasses any suitable elongated linear expedient such as slings, straps, rope and the like capable of performing the lift function.
Because manual operation of latches has been avoided efficiency in pipe laying has been increased. Moreover, a greater range of pipe sizes may be accommodated by a single adjustable pipe lifter.